Distance of 1.5 meters not enough for social distancing measures, study reveals

What is a safe distance that one should follow for social distancing in times of coornavirus COVID-19 pandemic? A recent study tried to find the answer to the question, taking the potential aerodynamic effects into account. The aerodynamic effects are introduced by person movement, such as walking fast, running and cycling. The preprint of the paper ‘Towards aerodynamically equivalent COVID-19 1.5 m social distancing for walking and running’, is a detailed study which investigates whether a first-person moving nearby a second person at 1.5 m distance or beyond could cause droplet transfer to this second person.

Previous research has shown that the spread of COVID-19 virus can occur effectively through saliva, often in the form of micro-droplets. When a person sneezes, coughs or even exhales, he or she is emitting small droplets – often too small to see with the naked eye – that can carry the virus. The receiving persons can be infected by inhaling these droplets, or by getting these droplets on their hands and then touching their face. That is why during the COVID-19 crisis, countries worldwide have declared a “social distance” of about 1.5 m to be kept between individuals. This is considered important and effective because it is expected that most of the droplets indeed fall and reach the floor and/or evaporate before having traveled a distance of 1.5 m.

The typical social distancing rules applied by most of the countries range within 1-2 meters between two persons.  However, this social distance has been defined for persons that are standing still. It does not take into account when you go for a walk, bike ride or run. The aerodynamic effects introduced by person movement leaves the trail runner at high risk. When someone during a run breathes, sneezes or coughs, those particles stay behind in the air. The person running behind you in the so-called slip-stream goes through this cloud of droplets.

As mentioned earlier, it is often assumed that most of the respiratory droplets fall and reach the floor and/or evaporate before having traveled a distance of 1.5 m, which is what has inspired the COVID-19 social distance of 1.5 m. However, micro-droplets have very little inertia and when two people are walking or running in each other’s vicinity, even at 1.5 m distance, due to the airflow patterns and people movements, these micro-droplets could be transferred from person A to person B due to the airflow patterns generated by the persons’ movement.

The researchers concluded that the exposure increases as the distance between leading and trailing person decreases. This suggests a safe distance for social distancing while walking, running or bike riding can be achieved, either by avoiding to run, walk or ride in the slipstream of the leading person and maintaining the 1.5 m distance or by keeping larger social distances, where the distance increases with the walking or running speed. The study however strongly suggests the best way is to stay out of the slipstream of the leading person.

According to the results of the research, it is advised that for walking, a distance of about 5m leads to no droplets reaching the trailing walker. For running and slow biking, this distance should be at least 10 m. Similarly, for hard biking, the distance should be at least 20 meters. Also, when passing someone it is advised to already be in different lane at a considerable distance e.g. 20 meters for biking.